Cool - thanks - that's good to know. I suppose by "the clamp may be enough," I thought the seat post clamp/fixing bolt could potentially provide enough stability regardless of whether the tube is butted or not. It sounds like that's the case given the seat doesn't end up erroneously high off the frame, the clamping mechanism is properly secured to the frame, the seat tube is properly tightened, and nothing else is problematic.
I'll probably go pretty minimal on the reaming. The outer wall thickness is 1mm at the edge, so 26.8-ish width seat tube should be ok.
**updated to fix grammar, oops
Last edited by bikingman; 07-22-20 at 09:06 PM.